Antennas for use under hostile environmental conditions, as is the case with antenna systems in mobile satellite communication, should be covered to prevent soiling or damage, regardless of whether they are portable or mounted on aircraft or other vehicles.
German patent document DE 10 2010 019 081 A1 shows an antenna designed as an array of horn antennas.
Depending on how the antenna is used, the range of conditions concerning which protection is required can include humidity, rain, sand, dust, chemicals, lightning, collisions with birds (in the case of airplanes) and many more. The electrical or high-frequency performance capacity of the radome (i.e. the cover or structure protecting the antenna) of the antenna is also important. This is indicated by electrical losses and suppression of cross-polarization.
The electrical losses are both reflective and dissipative in nature. Whereas the dissipative losses arise from the dielectric properties of the materials used, the reflections are defined by the quality of the high-frequency design. A skillful selection of materials, geometries and structures can minimize the reflective losses for the desired area of use and frequency range.
According to the state of the art, multi-layer sandwich structures of different composite and similar materials may be selected for a cover (i.e. a radome) for antennas.
DE 199 02 511 A1 discloses a basic design and function of a cover for antennas. A conventional sandwich-type radome has three interconnected layers: an inner liner, a radome core (having a thickness equal to ¼ of the wavelength, smallest possible dielectric constant) and an outer lining. In the case of two reflective layers spaced apart one behind the other at a distance of ¼ of the wavelength, the two resulting sub-reflections cancel each other out, since the phase difference of the two sub-waves equals 2*¼ of the wavelength, i.e. 180°. This keeps the reflections of the wave at the cover at a low level. Manufacturing these radomes requires a corresponding knowledge of adhesion, laminating and composite techniques, and also a well-balanced selection of the different materials.
In some applications, such as in airplanes, the radome is curved to improve the aerodynamic properties of the antenna mounted on the fuselage. For example, WO 2014/005691 A1 discloses that a radome (i.e. the cover of an antenna) can display polarization isotropy due to a curvature, which can result in marked changes in the axial ratio of circularly polarized signals passing through the radome. DE 10 2010 019 081 A1 discloses a radome that has been aerodynamically optimized.
United States Patent Application No. 2010/0309089 A1 discloses an antenna with several dipole elements. The dipole elements are provided with a cover that has a honeycomb structure, thereby forming partitions between the dipole elements and an individual radome for each dipole element.